It has come to be pointed out that one of the causes of the global warming is a greenhouse effect of CO2, and it has became an urgent task, also internationally, to provide a countermeasure for CO2 to protect the global environment against the warming. CO2 is generated by any human activities combusting fossil fuels, and there are increasing demands for suppressing CO2 emissions. Along with such an increasing demand, researchers are energetically investigating methods for reducing and recovering CO2 included in flue gas, applicable to a power plant that consumes a large amount of fossil fuels, such as a thermal plant. In such a method, flue gas emitted from a boiler is brought into contact with an amine-based CO2 absorbent to allow such absorbent to absorb the CO2, and the recovered CO2 is stored therein without being released into the air. As processes for reducing and recovering CO2 from the flue gas using the CO2 absorbent, a carbon oxide recovering system is used that brings flue gas into contact with the CO2 absorbent in an absorber, heats an absorbent that has absorbed CO2 in a regenerator, isolates CO2 as well as recycling the absorbent, and circulates the absorbent back to the absorber and reuses the absorbent therein.
In the carbon dioxide recovery system, the absorbent absorbs carbon dioxide included in the gas in the absorber, then the regenerator heats the absorbent to separate the carbon dioxide from the absorbent, and recovers the carbon dioxide thus separated. The absorber uses the regenerated absorbent in a cyclic manner.
To separate and recover the carbon dioxide in the regenerator, the absorbent needs to be heated in a reboiler. Therefore, heating steam at a predetermined pressure needs to be supplied in the reboiler.
Japanese Patent Application Laid-open No. H3-193116 discloses a method to use part of the steam generated in power plants and regenerate steam for this purpose.